Stress Activates Light-Emitting Nanowires

Enabled by the material’s hexagonal wurtzite structure, this discovery could enable novel devices that function as LEDs or light detectors, depending on whether they are compressed or stretched, according to investigators at IBM Research in Zurich. Current technologies use different materials to realize these two distinct functions: silicon or germanium for light detection and III-V semiconductors for light emission.

“We have now discovered that when you pull the nanowire along its length … the material has a direct bandgap and it can emit light very efficiently,” said Dr. Giorgio Signorello of IBM. “When instead you compress the length of the wire, its electronic properties change and the material stops emitting light. … We call this state pseudo-direct: The III-V material behaves similarly to silicon or germanium and becomes a good light detector.”

A team at the Norwegian University of Science and Technology supplied the nanowire material. Led by Dr. Helge Weman, researchers there have been developing ways to grow nanowires from semiconductors and studying their properties since 2010. Over the last two years, they have been growing GaAs nanowires on graphene using molecular beam epitaxy.

“We are showing how to use graphene to make much more effective and flexible electronic products, initially solar cells and white [LEDs]. The future holds much more advanced applications,” Weman said. Those applications include pressure sensors or electricity harvesting.